Many chairs which are used in a commercial environment, such as office chairs, chairs for computer data entry operators and chairs for operators of industrial plant process control equipment, are adjustable so that the chair will provide comfortable support to the user for an extended period of time. Accordingly, such chairs typically have a mechanism for adjusting the height of the chair. In addition, the chairs may include a mechanism for permitting the back support member of the chair to tilt relative to the seat member. Further, the chairs may provide a mechanism to permit the seat member of the chair to tilt so that the chair may be rocked backwards and/or forwards.
Typically, office chairs comprise a wheeled base, the seat member of the chair (which may include a back rest member) and a support leg extending between the wheeled base and the seat member. The height adjustment mechanism may employ a telescoping pneumatic cylinder which forms a part of, or may consist of, the support leg. These cylinders have a valve release pin provided thereon. The cylinder is generally in a locked condition but, when the valve release pin is depressed, the cylinder is unlocked typically permitting it to telescopically extend upwardly due to the force exerted by the pressurized fluid in the cylinder or contract downwardly due to, for example, a user sitting in the chair.
One mechanism which has been utilized to provide a tilt mechanism for the seat member of a chair comprises mounting the seat member on the support leg. A spring is provided so as to bias the seat member to the horizontal position. When the user leans backwardly in the chair, the users exerts a force greater than the biasing force of the spring thus causing the seat member to tilt rearwardly. An arm member positioned under the seat member may be used to lock the chair into the at rest, horizontal position. One disadvantage with this design is that the chair may not be fixed in an inclined position. Accordingly, if the user wishes to maintain the chair in an inclined position, they must continuously exert pressure against the spring.
Buchacz (U.S. Pat. No. 5,024,484) discloses an adjustable sitting device. The seat and/or back rest member of this device are turnable about an axis that is essentially coincident with an imaginary axis through the hip joints of the user. Slide members are provided so that the seat and back rest members of the chair are mounted for slidable movement with respect to each other. Movement of these members is controlled by locking means which interacts with the slide members and a gas cylinder.
Ishida (U.S. Pat. No. 4,383,714) discloses a rocking movable chair. The chair has a leg portion on which is mounted a circular arc surface. The seat member is mounted for travel along the circular arc surface. A spring is provided to bias the seat member in one direction during the rocking movement. A locking device utilizing a gas cylinder is provided to lock the rocking movement at a desired position.
Meiller et al (U.S. Pat. No. 4,743,065) discloses an office chair, the back rest member of which and the seat member of which may be adjusted by means of gas spring unit. Meiller et al discloses a locking member which utilizes a single actuating lever to adjust the inclination of the back rest member as well as the seat member.
Various control linkages for height adjustment mechanisms are known in the art. Examples of these include Kuhn et al (U.S. Pat. No. 5,069,496), Knapp (U.S. Pat. No. 4,408,800), Slabon et al (U.S. Pat. No. 4,076,308), Wirges et al (U.S. Pat. No. 4,072,288), Knoblauch et al (U.S. Pat. No. 4,373,692) and Lai (U.S. Pat. No. 5,222,783).
Numerous means have been used to control the inclination of the chair back member. These include various biasing means as well as the use of pneumatic cylinders. See for example Meiller et al (U.S. Pat. No. 4,743,065), Lei et al (U.S. Pat. No. 5,137,330), Kuhn et al (U.S. Pat. No. 5,069,496), Knapp (U.S. Pat. No. 4,408,800), Simpson (U.S. Pat. No. 4,681,369), Lai (U.S. Pat. No. 5,222,783), Slabon et al (U.S. Pat. No. 4,076,308) and Hiramatsu (U.S. Pat. No. 3,284,135).
Generally with the foregoing devices, the locking devices are adjusted by a lever or other mechanism which is positioned beneath the seat of the chair. Accordingly, the user must extend their arm downwardly and then transversely to a position underneath the seat to grasp the lever so that they can actuate the mechanism. This operation tends to be difficult particularly if the chair has a large, bulky arm. Since the use of these devices typically includes a biasing means to bias a chair to a preset position, the operator must move the actuating lever to the actuating position and hold the lever in that position while sitting in the chair so as to set the chair in the desired position. As this may require the operator to bend or stoop over, it is difficult to set the inclination of the chair accurately. This is also problematic if the operator has a back problem which prevents such movement.
Nelson (U.S. Pat. No. 4,595,237) discloses an actuating control for a seat height adjustment mechanism. The mechanism of Nelson uses a pivotally mounted lever positioned on the bottom of the seat number. Nelson still requires users to extend their arm downwardly beneath the seat to actuate the lever.